3General information Halogen Atomic radius (nm) Ionic radius (nm) Melting Point (oC)Boiling Point (oC)Density (g cm-3)Abundance on Earth (%)Fluorine0.0720.133-220-1881.110.062Chlorine0.0990.181-101-34.71.560.013Bromine0.1140.195-7.258.83.120.0003Iodine0.2161141844.93Astatine-302380Trace
4Characteristic properties Very reactive non-metalsHigh electronegativityHigh electron affinityBonding and Oxidation statesColour
5Electronegativity Element EN value F 4.0 Cl 3.0 Br 2.8 I 2.5 A measure of the attracting ability of bonding electrons.Due to their large effective nuclear charge,halogens are the most electronegative elementin the periodic table.
6Electron Affinity Element EA kJ/mol F -348 Cl -364 Br -342 I -285 Generally high electronaffinity. All are exothermic.X(g) + e- X-(aq)
7Bonding and Oxidation State ns2np5Ionic or covalent bond with oxidation state –1 or +1 (F shows –1 only)Except F, all other halogens can expand their octet by using the low-lying, vacant d-orbitals to form bonding. Their oxidation states range from –1 to +7.
8Bonding and Oxidation State nsnpnd(+3 states)HClO2, ClO2-nsnpnd(0, +1, -1 states)Cl2, Cl-, OCl2
9Bonding and Oxidation State nsnpnd(+7 state)Cl2O7, HIO4nsnpnd(+5 state)HClO3, HBrO3, I2O5
10Colour Element Colour In Standard State In Water In 1,1,1-trichloroethaneFPale yellowClGreenish yellowYellowBrReddish brownOrangeIViolet blackBrownViolet
13Variation in properties of Halogens F Cl Br I At400-300(Temp. oC)b.p.m.p.m.p./b.p. increase as Mr increasebecause Van der Waals’ Force increasewith Mr
14Electronegativity 4.0 4 F form ionic compound with –1 oxidation state. F Cl Br I43214.03.02.82.5F form ionic compoundwith –1 oxidation state.I shows highly positiveoxidation states withmore electronegativeelement.e.g. KIO4
15Electron affinity EA decrease from Cl to I due to increasing atomic size which lowersthe nuclear attraction tothe added electron.F has exceptional lowerEA because its 2nd shellis already crowded with7 e-, the additional e-will experienced a greatere-e repulsion than otherhalogens.F Cl Br I280320340
16Variation in Chemical Properties of elements All are good oxidizing agents. (F2>Cl2>Br2>I2)½ X2(std.state) X-(aq)X(g)X-(g)HatomHHEAHhydHHatomHEAHhyd=+
17Oxidizing power Hatom HEA Hhyd H Oxidizing strength Element F 79.1 -348-506-774.9Cl121-364-607Br112-342-335-565I107-314-293-500HatomHEAHhydHOxidizingstrength
18Oxidizing properties Oxidation of metals Standard electrode potential (V)Cl2+e-Cl-1.36Br2+e-Br-1.07I2+e-I-0.54Fe3++e-Fe2+0.77Oxidation of metalsa. F2 oxidizes all metals including Au and Ag.b. Cl2 oxidizes common metals such as Na and Cu.Reactions with Fe2+(aq)2Fe2+ + Cl22Fe3+ + 2Cl-2Fe2+ + Br22Fe3+ + 2Br-2Fe3+ + 2I-2Fe2+ + I2
19Oxidizing properties 3. Reaction with phosphorus 2P + 3X2 2PX3 F2 and Cl2 form PX5 as they have high oxidizingStrength. They combine with P to exhibit its maximumoxidation state.Br2 and I2 form PX3 only.
20Reaction with water Fluorine oxidizes water to form HF and O2 2F2 + 2H2O 2HF + O2Chlorine undergoes disproportionation(self oxidationand reduction) to form HCl and HOCl.Cl2 + H2O HCl + HOCl
21Reaction with water A mixture of Cl2(aq), HCl(aq) and HOCl(aq) is called chlorine water.OCl- , chloric(I) ionStrong oxidizing agent with bleaching propertyOCl- + dye (coloured) Cl- + dye (colourless)Unstable to heat and light2OCl- O2 + 2Cl-
22Reaction with water Br2 is only slightly soluble in water. Br2 (aq) + H2O (l) HBr(aq) + HOBr(aq)OBr-(aq) is unstable and with bleaching property:2OBr- O2 + 2Br-2. OBr- + dye(coloured) Br- + dye(colourless)
23Reaction with water I2 does not react with water and only very slightly soluble in water.I2 is more soluble in ethanol or in KI(aq).I2(aq) + I-(aq) I3-(aq)
24Reaction with alkalis All halogens react with aqueous alkalis and disproportionate in it. The products depend ontemperatureandconcentration of the alkalis.
27Reaction with alkalis The reverse reaction of I2 and KOH is used to prepare standard iodine solution for iodometrictitration. Know amount of iodine is generated bydissolving known quantity of KIO3 in excess KIand H+.5KI + KIO3 + 3H+ 3I2 + 6K+ + 3H2O
32Halides + Ag+(aq) Ion Action of AgNO3= Effect of Standing in sunlight Effect of adding excess aq. NH3Cl-White ppt.Turns greyWhite ppt. dissolvesBr-Pale yellow ppt.Turns yellowish greyPale yellow ppt. slightly dissolvesI-Yellow ppt.Remains yellowYellow ppt. does not dissolve
33Relative acidity of HX Hydrogen Halide Dissociation constant Degree of dissociation in 0.1M solutionHF7x10-40.085HCl1x1070.920HBr1x1090.930HI1x10110.950
34Relative Acidity of HX H HX(aq) H+(aq) + X-(aq) H5 H6 H1 H+(g) X-(g)H3H4H2HX(g)H (g) X (g)
35Relative Acidity of HX H1 H2 H3 H4 H5 H6 H TS G HF485661311-333-1091-515-14-2915HCl18431-348-381-60-13-47HBr21366-324-347-64-4HI23299-295-305-584-62H1H2H3H4H5H6HTSGExplanation of weak acid strength of HF:HF has the greatest bond dissociationenergy and exceptionally smallelectron affinity. It has the leastexothermic H.Due to formation of strong hydrogenbond and greatest degree of hydration,HF has the smallest decrease of TS.
36Anomalous behaviour of HF According to La Chatelier’s Principle, the degreeof dissociation of a weak acid increases with dilution.HA H+ + X-However, the acidity of conc. HF is greater thandilute HF. Why?In conc. HF, HF molecules form dimers H2F2 byhydrogen bond. The acid strength of H2F2 isstronger than HF.H2F2 H+ + HF2-
37Uses of Halogens and Halides TeflonNa2SiF6 or NaF is used to fluoridate drinking water.Chlorine bleach, sterilization of water, PVC.Anti-knocking agent (leaded petrol)AgBr coating in filmIodine tinctureAgI in coating film